An optical communication system transmits information encoded in optical (light) signals from an optical transmitter to an optical receiver over one or more optical fibers. An optical transmitter commonly includes a light source, such as a laser or light-emitting diode, as well as optical and mechanical elements for coupling the light source to an optical fiber. Similarly, an optical receiver commonly includes a light receiver, such as a photodiode, as well as optical and mechanical elements for coupling the light receiver to an optical fiber. The optical elements commonly include lenses and may also include mirrors or similar reflective elements that redirect the optical paths.
Optical transmitters and receivers are commonly modularized to facilitate coupling to the fiber and to the systems with which optical signals are to be communicated. An optical transmitter or receiver module commonly includes a housing, which may be sealed to inhibit contamination of optical paths by dust or similar airborne matter. The housing may include a port to which the end of an optical fiber can be coupled. Optical transceiver modules that include both an optical transmitter and optical receiver are well known and exist in a number of different form factors. In some optical communication modules, lenses or other optical elements are unitarily molded along with other portions of the housing, which may be made of an optically transparent plastic material.
As illustrated in FIG. 1A, it is known to form an optical assembly 10 by a method that includes placing a lens device 12 over one or more opto-electronic and electronic devices 14 mounted on a surface of a printed circuit board (PCB) 16. Devices 14, which can include, for example, a vertical cavity surface-emitting laser (VCSEL) or a photodiode, and an associated integrated circuit chip, can first be mounted on the surface of PCB 16. A robotic pick-and-place machine (not shown) may align the VCSEL or photodiode on PCB 16 with respect to fiducial markings 17 that are sensed through a machine-vision feedback system. The alignment tolerance achieved by the pick-and-place machine is commonly on the order of tens of microns.
Lens device 12 includes a reflector 18 and other optical elements that redirect light at a 90-degree angle between the VCSEL and an optical fiber port 20. After lens device 12 is placed over devices 14, the optical paths are precisely aligned using an active alignment method. In the active alignment method, light is introduced (by external equipment, not shown) through optical fiber port 20, and the amplitude of the electronic signal produced by one of opto-electronic devices 14 in response to the light is monitored (by external equipment, not shown) as lens device 12 is moved about the plane parallel to the surface of PCB 16 in small increments. When the measured amplitude is a maximum, the movement of lens device 12 is halted at the corresponding position, and lens device 12 is secured at that position to the surface of PCB 16. As shown in FIG. 1B, lens device 12 can be secured by applying epoxy 22 between the base of lens device 12 and the surface of PCB 16. Although epoxy 22 is depicted in FIG. 1A for purposes of illustration as a rectangular bead on which lens device 12 can be placed, small dots of UV-curable epoxy (not shown) may instead be used to initially tack lens device 12 to PCB 16. A bead of structural epoxy is then applied around the perimeter after the initial tack bonds have been UV-cured. The assembly then may be placed in an oven to cure the bead of structural epoxy. An end of an optical fiber 24 is shown coupled to port 20 in FIG. 1B.
A disadvantage of the above-described method of forming optical assembly 10 is that the active alignment and epoxy curing steps take significant amounts of time, thereby potentially impacting manufacturing throughput (i.e., units per hour produced). Another disadvantage of the above-described method is that performing active alignment and dispensing the epoxy are commonly performed manually, i.e., under direct control of a person, which can result in a greater percentage of defective assemblies (i.e., lower manufacturing yield) than a more automated method. It is common, for example, for elements of lens assembly 10 to drift out of optical alignment with one another while the epoxy cures. A method of forming an optical assembly that maximizes throughput and yield would be desirable.